(Adds background on dispute)
WASHINGTON, March 19 (Reuters) - U.S. President Donald Trump on Tuesday accused social media platforms Facebook, YouTube and Twitter of favoring his Democratic opponents over him and his fellow Republicans.
"But fear not, we will win anyway, just like we did before! #MAGA," he said in a tweet. MAGA refers to Trump's 2016 campaign slogan, "Make America Great Again."
Facebook Inc and Twitter Inc declined to comment. Alphabet Inc's Google, which owns YouTube, did not immediately comment.
The president and other conservatives have repeatedly complained that these big tech platforms treat them unfairly.
Trump has previously accused Twitter of restricting the visibility of prominent U.S. Republicans, without any providing evidence, and the avid social media user has promised to investigate the company's practices.
Trump and other conservatives say Twitter targets fellow Republicans with a practice dubbed "shadow banning," limiting the visibility of a Twitter user, including in the platform's auto-populated dropdown search box.
Representative Devin Nunes of California has sued Twitter over the alleged practice, according to court documents.
Twitter Chief Executive Officer Jack Dorsey has said that algorithms have been changed to fix that issue.
The Justice Department held a meeting last fall between federal officials and state attorneys general to discuss allegations that conservative ideas are suppressed online, but so far no concrete action has been taken as a result. (Reporting by Diane Bartz and David Shepardson; Editing by Nick Carey)